They're not commercialy available as far as I'm aware but there is a guy selling Canon-Adaptall adapters he has made on e-bay.

From what I can gather there isn't a traditional stopping down lever on the Canon EOS onwards (or Nikons?) so your lens must be capable of being stopped down manually. There will be a slide lever near the base of your Adaptall lens saying A (auto) and M (manual). You would have to set the lens to A to focus it & then to M to close the aperture.